The invention is related to the art of image processing. The invention will be described in reference to electrophotographic applications, such as, for example, xerographic imaging. However, the invention can be applied in other areas, such as, for example, video image processing and lithographic systems.
In electronic imaging systems, images, such as, for example, pages of a document, are described in terms of high-level image or page description languages (PDL). Postscript™ is one such page description language well known in the art. In order to render an image, an image processor generates a binary image from the page description language description of the image. The binary image or bit map is in the form of a grid work or raster of mark/no mark decisions. The generation of a binary image from a page description language version of the image is referred to as raster image processing (RIP). In electrophotographic systems, a raster output scanner controls a marking engine to place spots of ink, toner, or other colorants on a print medium according to the binary mark/no mark decisions indicated in the bit map.
To achieve high print quality, it is necessary to RIP documents to a high resolution. Typically, these resolutions are symmetric. For example, resolutions such as 1200×1200, 1800×1800, or 2400×2400 dpi are common. For instance, these symmetric resolutions are supported by standard Postscript™ interpreters. However, due to mechanical constraints and economic factors, raster output scanner electronics are often designed to support asymmetric high addressable resolutions, such as 1200×600, 2400×600, and 4800×600 instead of the symmetric resolutions mentioned above. Occasionally, the reverse situation applies. In either case, a resolution conversion is required to make the output of the raster image processor (RIPer) compatible with the raster output scanner (ROS) electronics.
Previously, techniques such as perspective projection (PP) were used to provide resolution conversion. Unfortunately, PP can create quantization errors and discard positioning information. This may result in reduction in print quality. Additionally, PP cannot be easily implemented in-line; it requires use of error diffusion, dramatically increasing the gate count and complexity. For more information on perspective projection, see U.S. Pat. No. 5,655,061 to Tse, et la., entitled, System and Method for Providing a High-Addressable Printing System.
For the foregoing reasons, there is a desire for a resolution conversion system and method that can be easily implemented in-line and maintain position information while minimizing quantization error generation.